When powered on or during handover, a mobile station such as a mobile phone can communicate by appropriately selecting and using a cell (base station). Selection of a cell by a mobile station is called a cell search. In a cell search, a mobile station selects the optimal cell to be connected to when powered on. Specifically, each cell is identified by a unique scrambling code, and a cell search is performed by a mobile station detecting the scrambling code of the cell that transmits the signal with the greatest received power in a downlink.
A conventional technology related to this is a three-step initial cell search method in OFCDM (Orthogonal Frequency and Code Division Multiplexing) (see Patent Document 1, for example).
With the conventional technology described in Patent Document 1, scrambling codes can be fast detected by grouping scrambling codes into a number of groups. Specifically, in the first step, symbol timing is detected by means of guard interval correlation; in the second step, frame timing and a code group are simultaneously detected by calculating correlations between temporally adjacent OFDM symbols; and in the third step, a scrambling code is identified by means of correlation calculation from between pilot symbol and scrambling code candidates belonging to the code group detected in the second step.
FIG. 1 shows a conventional OFCDM frame configuration. As shown in FIG. 1, there are consecutive pilot symbols in the time domain at a frame boundary, and a code group sequence indicating a scrambling code group is multiplied by a frame-end pilot symbol.
FIG. 2 shows conventional second-step processing of a cell search performed by a mobile station. The mobile station performs frame timing and scrambling code group detection by calculating correlations between a sequence extracted by differential demodulation between adjacent symbols and a code group sequence of all code group candidates. A code group and frame timing are detected simultaneously by detecting the code group and timing for which the maximum correlation value between these adjacent pilot symbols is calculated.    Patent Document 1: Unexamined Japanese Patent Publication No. 2003-244763